Replying to Tv tuner question (premium channels?)

I'm looking to get the ATi 650 pci-e tuner card. From what I read you can use it for analog and HD(via clearQAM).

Now my question is can I use it to get premium cable channels... HBO and such. Ive seen people ask this question trying to get it without a top set box. I have a top set box for comcast. Its set up in my basement to my little theatre. The box come with a variety of connections in the back of the box..  Right now I have the cable in then I'm using a HDMI to connect the box to the receiver. My question is if use the cable out of the top set box to my tuner will the cable box have to be on the same channel as the tuner?

If anyone has tried this please relay your findings or if anyone has any information and could point me in the right way your help is greatly appreciated!

Thanks